Hook latch

ABSTRACT

A latch for equipment cabinet doors adaptable for joining wall panels and like structures includes a cam having a hook mounted thereon for engaging a sill pin to latch the doors or structures. The latch further includes a trigger and a stop pin which engage shoulders on the cam to provide positive engagement and disengagement features to prevent malfunctioning of the latch hook during closing and opening, respectively. These features are set for proper operation before the latch can be disengaged during opening.

United States Patent In] 3,851,922 McCoy Dec. 3, 1974 [54] HOOK LATCHFOREIGN PATENTS OR APPLlCATlONS 1 1 lnvfimofl Robert Gordon MCCOY,whiPPflny, 100,095 10/1940 Sweden 292/111 [73] Assignee: Bell TelephoneLaboratories Primary EXamin@rRihard E- Moore Incorporated, Murray Hill,Attorney, Agent, or FIrm-A. D. Hooper [22] Filed: Jan. 7, 1974 Appl.No.: 431,032

[57] ABSTRACT A latch for equipment cabinet doors adaptable for joiningwall panels and like structures includes a cam having a hook mountedthereon for engaging a sill pin to latch the doors or structures. Thelatch further includes a trigger and a stop pin which engage shoulderson the cam to provide positive engagement and disengagement features toprevent malfunctioning of the latch hook during closing and opening,respectively. These features are set for proper operation before thelatch can be disengaged during opening.

5 Claims, 9 Drawing Figures PATENTEL BEE 31974 SHEEI 1 OF 2 PATENTEL BEEW4 sum 2 or 2 HooK LATCH BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to latches and more particularly to ahook latch for doors of equipment cabinets and adaptable for joiningwall panels and the like.

2. Description of the Prior Art Numerous latches of locks have beendesigned for latching the doors of equipment cabinets and the like. Manyof these latches utilize an eccentric to operate a hook which engages asill pin to thereby latch the doors. However, these existing latcheshave various limitations which reduce their-usefulness on equipmentcabinets which are installed in publicly accessible locations and whichrequire good security to prevent unauthorized entry into the cabinet.For example, many of the known latches include no positive engagement ordisengagement features which insure proper operation of the latch. Evenwhere a positive engagement feature is provided, such feature is readilynullified if the latch is not rotated to the fully open position duringthe opening cyclebecause this feature is set up only at the very end ofthe opening cycle and often requires substantial torque in existinglatches. Latches not having a positive disengagement feature may fail toopen properly if excessive resistance is encountered during the openingcycle. Furthermore, latches not having positive engagement features orin which the positive'engagement-feature is not activated because ofinsufficient opening rotation or torque may appear to close properlythough, in fact not being engaged.

A further limitation of hook-eccentric type latches is their tendency torelease with only partial rotation of the eccentric coupled with theusers tendency to stop turning the eccentric when release occurs. Uponsubsequent closing, the hook frequently fails to engage the sill pin butgives no indication-of lack of engagement.

Another limitation of some existing latches includes mounting on theexterior of the cabinet doors which makes the latch readily accessibleand vulnerable to tampering.

Still another limitation is that many existing latches do not provide asufficient pulling force when used with L-shaped doors which are hingedout of the front plane of the doors where the latch is located, and manydo not accommodate reasonable misalignment of the doors.

Accordingly, it is an object of this invention to provide a cabinetlatch having positive engagement and disengagement features of muchgreater reliability. Another object is to improve latches for cabinetdoors so that such latches provide greater security for the cabinets.

SUMMARY OF THE INVENTION The foregoing objects and others are achievedin accordance with the invention ,by a latch for a cabinet whichincludes a sill pin and a hook for engaging the sill pin to lock thecabinet. The hook is frictionally mounted on a cam which rotates to movethe hook into and out 'of engagement with the sill pin. The hookincludes a first pin which engages a tab on the latch cover to causerotation of the cam with respect to the hook so that the hook can beextended away from the sill pin during the. initial unlocking movement.A spring biased mating therewith to operate the latch.

trigger mounted on the hook includes a lip which engages a shoulder onthe cam immediately prior to complete extension of the hook from thesill pin during this initial unlocking movement. This provides apositive engagement force during a subsequent locking movement. An armof the trigger engages the sill pin to pivot the lip away from theshoulder and allows completion ofthe locking movement when the hook andsill pin are properly engaged. The shoulder on the cam contacts a secondpin on the hook during unlocking to provide a positive disengagementforce if the hook encounters excessive resistance during thedisengagement movement. The hook and sill pin have cam or taperedsurfaces thereon which return the hook to the disengage position if anattempt is made to close the cabinet doors when the hook is in an engageposition.

BRIEF DESCRIPTION OF THE DRAWING The invention will be more fullycomprehended from the following detailed description and accompanyingdrawing in which: i

FIG. 1 is an exploded perspective view partly broken away of oneembodiment of the latch of this invention mounted on cabinet doors asviewed from the inside of the cabinet;

FIG. 2 is an elevation view of the latch area of the cabinet doors asviewed from the outside of the cabinet with the doors latched; and

FIGS. 3 through 9 are schematic illustrations of the latch mechanism atvarious positions during the opening and closing thereof as viewed fromthe inside of the cabinet.

DETAILED DESCRIPTION FIG. 1 shows the latch 101 of this inventioncomprising a sill pin 103 and a latch assembly 102, respectively,mounted on the inside of cabinet doors 104 and 106. The only portion oflatch 101 which is visible and accessible from the outside of thecabinets when doors 104 and .106 are latched or closed as indicated inFIG. 2 are the head 13 of a stepped shaft 12 and the ends of hardware108 such as rivets or screws used for mounting latch 101 to doors 104and 106. The latch is operated, i.e., opened and closed, therebyunlatching and latching doors 104 and 106, by placing an appropriatetool over shaft head 13 and rotating head 13 until pointer 52 thereon isaligned with an appropriate index 54 or 56 indicating closed and openpositions, respectively. Head 13 is substantially flush with the outsidefront face of door 106 and is accessible through hole 111 in door 106.Accordingly, latch 101 offers good security against tampering in thathead 13 which is the only accessible part, can be given any desired typeof configuration which requires a special tool for Although latch 101can be utilized with any type of cabinet doors, it isvery advantageouswhen used with L-shaped doors which have hinges lying out of the planeof front faces 109 and 110 of doors 104 and 106. Latch 101 provides astrong pulling force in the plane of front faces 109 and 110 to tightlyjoin the overlapping edges of doors 104 and 106 in this plane; Thisfeature would also make a latch in accordance with this invention usefulin joining wall panels and the like as previously mentioned.

Sill pin 103 includes a substantially L-shaped bracket 3 which ismounted to the inside of door 104 by appropriate hardware 108 such asrivets or screws. A stud 4 extends inward substantially perpendicular tobracket 3 and door 104. Stud 4 includes a tapered face 5 and a neckeddown portion 6 which joins it to bracket 3.

Latch assembly 102 includes a base plate or bracket 60 by which it ismounted to the inside of door 106 by hardware 108. Plate 60 includesfour legs or flanges 62 extending therefrom to which a cover 64 ismounted by hardware 66 to define a chamber or space therebetween. Shaft12 is journaled in cover 64 and plate 60 for rotation therein byappropriate bushings or bearings 68 known in the art.

Secured to shaft 12 between plate 60 and cover 64 for rotation withshaft 12 is a cam or eccentric l0. Cam 10 is mounted off center withrespect to shaft 12 so that its periphery follows an eccentric path withrespect to shaft 12. Cam 10 includes a circular hub portion 14 and acontoured portion 16 on which cam surfaces or shoulders 18 and 19 areformed for purposes to be discussed subsequently.

A hook member 2 having an end 72 adapted to embrace the necked downportion 6 of sill pin stud 4 when latch 101 is closed is mounted on hubportion 14 of cam 10. End 72 of hook 2 includes a tapered edge 74 havinga slope or taper matching the taper of face 5 on stub 4 for purposes tobe disclosed hereafter. A lip 76 is placed on the tip of end 72 tofurther insure that hook 2 remains in position about stud 4 when latch101 is closed.

An axial compressive or squeezing force along shaft 12 is suppliedbetween hook 2 and cam 10 by forming the portion of cover 64 in whichshaft 12 is mounted in the form of a cantilever spring 65 as shown. Aspacer washer 70 is rotatably mounted on shaft 12 and contacts hook 2about the periphery of hub 14 to squeeze hook 2 between washer 70 andthe shouldered portion 16 of cam 10 by utilizing the compressive forceof spring 65. This establishes a frictional force or drive between cam10 and hook 2 which causes book 2 to rotate with cam 10 unless book 2encounters a resistance exceeding the frictional drive.

A trigger 24 is rotatably mounted on hook 2 by a stud 26 and is biasedbya spring 28 to tend to rotate with respect to hook 2 so that a lip 40on an arm 38 thereof engages shoulder 19 on contoured portion 16 of cam10. Trigger 24 includes a second arm '36 adapted to contact stud 4 topivot lip 40 on arm 38 away from contact with shoulder 19 as will beexplained subsequently.

Hook 2 includes two studs or pins and 22 extending outward therefromtoward cover 64. Cover 64 includes a tab or lip extending inwardlytoward hook 2 and adapted to contact pin 20 during aportion of theopening cycle of latch 101. Cover 64 also includes a cutout or slot 78along an edge thereof adapted for re ceiving stud 4 therein. Theentrance 79 to slot 78 advantageously can be tapered to guide stud 4into slot 78 when doors 104 and 106 are being closed.

The operation of latch 101 will now be discussed in detail withreference to FIGS. 3-9 which schematically represent the latch invarious positions, as viewed from the interior of the cabinet. during acomplete opening and closing cycle. In FIG. 3 the latch is shown fullyclosed with the end 72 of hook 2 fully engaging stud 4. In this positiondoors 104 and 106 cannot be moved any appreciable amount with respect toeach other but are held in a tightly closed or locked overlappingrelationship. In this configuration shaft 12 is rotated fullycounterclockwise (as viewed from the interior of the cabinet) untilpointer 52 on shaft head 13 is aligned with index 54. Further rotationof shaft 12 in the locking direction is prevented by the engagement ofpin 22 on hook 2 with shoulder 18 on cam 10.

To open latch 101, shaft 12 is rotated clockwise (as viewed from theinterior of the cabinet) thereby rotating cam 10 mounted thereonclockwise. As shown in FIG. 4, upon the initial rotation of shaft 12 andcam l0. hook 2 also rotates clockwise a very small amount as indicatedby arrow 32 because of the frictional drive between book 2 and cam 10.This initial rotation of hook 2 continues until pin 20 thereon contactstab or flange 30 which acts as a stop to prevent further rotation ofbook 2 until pin 20 can get by or escape from tab 30. At this point hook2 is still engaged with sill pin stud 4 and thus doors 104 and 106cannot be opened though their tightly closed relationship has beensomewhat relaxed. This initial rotation of hook 2 also allows acorresponding counterclockwise rotation of trigger 24 with respect tobook 2 because of the force of spring 28 to rotate arm 38 of trigger 24into closer proximity to cam 10.

After pin 20 contacts tab 30, the frictional drive between hook 2 andcam 10 is overcome. Thus upon continued clockwise rotation of shaft 12and cam 10, hook 2 does not rotate therewith but instead is forced orextended outward away from stud 4 by the eccentric motion of cam 10 asindicated by arrow 34 in FIG. 4. This extension of hook 2 outward fromstud 4 also causes pin 20 to move outward along tab 30 as indicated.Hook 2 remains in sufficient engagement with stud 4 during this outwardextension to maintain doors 104 and 106 in a locked configuration eventhough the doors can move with respect to each other an amount equal tothe extension of hook 2.

When hook 2 has been substantially fully extended, pin 20 reaches theedge of tab 30 and begins the escape therefrom as shown in FIG. 5. Thisrestores the frictional drive between hook 2 and cam 10 so that anysubsequent rotation of shaft 12 and cam 10 will produce rotation of book2. Just before pin 20 completes the escape from tab 30, cam 10 hasrotated clockwise allowing trigger 24 to rotate counterclockwise underthe influence of spring 28 sufficiently for lip 40 on trigger arm 38 todrop past the rear or trailing edge 42 of shoulder 19 to establish thepositive engagement feature previously mentioned and to be discussed inmore detail subsequently. It should be clear that this positiveengagement feature is set up or established before hook 2 completelyescapes sill pin stud 4 and Consequently before doors 104 and 106 can becompletely opened. Accordingly, this insures that during any subsequentclosure of latch 101, all parts must be properly positioned with respectto each other or the latch cannot be closed.

Continued rotation of shaft 12 and cam 10 from the position of FIG. 5produces a corresponding rotation of hook 2 in the direction of arrow 44completing the escape of pin 20 from tab 30 as indicated in FIG. 6because of the restored frictional drive between hook 2 and cam 10. Thisrotation continues until hook 2 completely disengages sill pin 4 so thatdoors 104 and 106 can be opened. After this complete disengagement hook2 can be further rotated until it contacts one of the frame legs 62 orsome other fixed stop such as the 5 and 7 hook 2 encounters sufficientresistance to overcome the frictional drive between it and cam 10, hook2 will stop and cam 10 will continue to rotate until the front edge 46of shoulder 19 thereon encounters pin 22. Thereafter cam 10 imparts apositive drive force to rotate hook 2 to the position shown in FIG. 7.This is the positive disengagement feature previously mentioned. Thispositive disengagement feature is especially important in situationssuch as when doors 104 and 106 do not mate satisfactorily and thus tendto cause hook 2 to bind. The positive drive'disengagement force insuresthat such binding can be overcome so that latch 101 can be fully opened.

When it is desired to close latch 101, shaft 12 and cam 10 are rotatedcounterclockwise. Hook 2 also rotates counterclockwise as indicated byarrow 48 in FIG. 8 because of the frictional drive between hook 2 andcam 10. Hook 2 is fully extended outward during this initial closingrotation. If at any time during this rotation hook 2 encounterssufficient resistance to overcome the frictional drive between it andcam 10, hook 2 will stop and cam 10 will continue to rotate until therear edge 42 of shoulder 19 engages lip 40 on trigger. arm 38.Subsequently cam 10 will apply a positive engagement torque or force tohook 2 through trigger 24 to force hook 2 to rotate therewith.

If excessive resistance to the rotation of hook 2 occurs before pinclears tab as indicated in FIG. 8, hook 2 may withdraw slightly causingpin 20 to be blocked or stopped by tab 30. Trigger arm 36 will then failto contact stud 4 andfurther closure is prevented.

Tab 30 can be designed with sufficient thickness 31 to minimize theangle of rotation during which such blockage could occur.

The counterclockwise rotation of cam 10, trigger 24 and hook 2 continuesuntil trigger arm 36 contacts sill pin st'ud 4 as shown in FIG. 8. Uponfurther counterclockwise rotation of cam 10, trigger 24 is rotatedclockwise as shown by arrow 51 because of the force exerted on triggerarm 36 by stud 4. This pivots lip 40 away from contact with rear edge 42of shoulder 19 and allows rotation of cam 10 and hook 2 until hook 2encounters stud 4 to stop the rotation thereof. Completion of thedisengagement oflip 40 from edge 42 occurs just before hook 2 contactsstud 4. At this point hook 2 is still substantially fully extended butis in engagement with stud 4 as indicated in FIG. 9. Doors 104 and 106can be moved with respect to each other an amount approximately equal tothe extension of hook 2 but cannot be completely opened. Upon subsequentadditional counterclockwise rotation of cam 10, book 2 does not rotatebut withdraws as indicated by arrow until it returns to its initialposition illustrated in FIG. 3.

If all parts of latch 101 are not properly positioned with respect toeach other the positive engagement feature prevents complete rotation ofshaft 12 and cam 10. For example, if an attempt is made to rotate cam 10and hook 2 to the closed position while doors 104 and 106 are open sothat stud 4 is not within engageable reach of hook 2, lip 40 on triggerarm 38 locks up cam 10 somewhat after the position shown in FIG. 8 isreached because trigger 24 is not pivoted in a direction to remove lip40 out of the path of edge 42 of shoulder 19 as occurs in normaloperation. Hence cam 10 and shaft 12 can be rotated slightly past theposition of FIG. 9 but cannot be rotated to the initial position of FIG.3. This will be made obvious by the latch operatorobserving that pointer52 is not aligned with index 54. The amount of rotation required by cam10 and shaft 12 in moving from the fully opened position of FIG. 7 tothe engaged but fully extended position of FIG. 9 is only a small.fraction of the total rotation required, i.e., most of the rotation ofcam 10 and shaft 12 occurs during withdrawal of hook 2 as depicted byarrow 50. A typical example is that shaft 12 rotates approximately 27 ingoing from the fully opened position of FIG. 7 to the engaged but fullyextended position of FIG. 9. On the other hand shaft 12 rotates about191 degrees during the withdrawal of hook 2 in going from the positionof FIG. 9 to initial the fully closed position of FIG. 3. Thus it isclear that pointer 52 will not remotely approach index 54 indicating alocked position unless the parts of latch 101 have been properlypositioned and the latch has operated normally. I

The edge 107 of door 106 fits inside the edge 108 of door 104 in normaloperation; If hook 2 is inadvertently rotated without doors 104 and 106being prop- .erly closed with respect to each other, pin 20 on hook 2engages tab 99 on cover 64 to prevent rotation of hook 2 significantlypast the position shown in FIG. 9. The subsequent closing of door 104will return hook 2 to the completely open and disengage positionapproximated in FIG. 6. This is accomplished when door 104 is swung intoposition over door 106 by tapered surface 5 on stud 4 contactingmatching tapered edge 74 on book 2 and applying a lifting force theretoto return hook 2 to the disengage position.

It should be clear from the foregoing that an operator can be assuredthat latch 101 has operated properly unless shaft 10 refuses to turn.The operator need only rotate head 13 of shaft 12 until pointer 52thereon is aligned with the appropriate index 54 or 56 in order todefinitely know that the latch is fully and properly closed or opened,respectivelyjlf the operator cannot rotate shaft 12, he knows that theparts of latch 101 are not properly positioned. The positive engagementfeature insuring proper closing of latch 101 during any subsequentclosing operation is automatically set up before latch 101 can becompletely opened. Thus this feature cannot be nullified or circumventedas it can be in existing latches.'The positive disengagement featureinsures that latch 101 can be opened regardless of any resistance orbinding which may be encountered. The tapered surfaces on hook 2 andstud 4 insure that latch 101 is positioned for proper operation even ifan attempt is made to operate latch assembly 102 while the cabinet doorson which latch 101 is mounted are open.

While the invention has been described with reference to a specificembodiment thereof, it is to be understood that various modificationsthereto might be made by those skilled in the art without departing fromits spirit and scope.

What is claimed is:

1. A latch comprising a sill pin; a rotary eccentric cam having a firstshoulder on the periphery thereof; a

hook member mounted on said cam and adapted to move into and out ofengagement with said sill pin in response to a rotation of said cam toclose and open said latch, respectively, a trigger rotatably mountedwith respect to said hook member and having a lip thereon adapted toengage said first shoulder on said cam to preventrotation of said cam toclose said latch until said cam, said hook member and said sill pin areproperly positioned with respect to each other, characterized in thatsaid latch includes:

first means for maintaining said hook member in engagement with saidsill pin until said lip has engaged said first shoulder and until saidhook member has been substantially fully extended when said latch isbeing opened; and

second means for removing said lip from engagement 7 with said firstshoulder after said hook member has moved into engagement with said sillpin when said latch is being closed.

2. Apparatus in accordance with claim 1 wherein said latch includes:

a spring for biasing said trigger in a direction to cause said lip toengage said first shoulder;

a cover having a tab thereon extending outward therefrom toward saidhook member;

said first means includes a first pin on said hook extending outwardtherefrom and adapted to contact said tab to prevent rotation of saidhook member with said cam during a substantial portion of said rotationof said cam when said latch is being opened, whereby said cam rotateswith respect to said hook member until said lip engages said firstshoulder; and

said second means includes an arm on said trigger adapted to contactsaid sill pin to pivot said lip away from contact with said firstshoulder.

3. Apparatus in accordance with claim 2 wherein said hook memberincludes a second pin extending outward therefrom and said cam includesa second shoulder, said first shoulder being adapted to contact saidsecond pin to provide a positive rotation force to said hook member whensaid hook member encounters resistance before said latch is fully openand to prevent further rotation of said cam in an opening direction whensaid latch is fully open. and said second pin being adapted to contactsaid second shoulder to prevent further rotation of said cam in aclosing direction when said latch is fully closed.

4. Apparatus in accordance with claim 3 wherein said latch is adaptedfor mounting on doors of a cabinet. said sili pin includes a taperedface and said hook mcmber has an end tapered to match said face of saidsill pin and adapted to contact said face to return said hook member toa position out of engagement with said sill pin when said hook member isrotated into a position for engaging said sill pin while said doors areopen.

5. A latch comprising, in combination:

a latch cover having an outstanding tab thereon;

a rotary eccentric cam having a shoulder on the periphery thereof;

a sill pin;

a hook member mounted on said cam and responsive to the rotation of saidcam to move into and out of engagement with said sill pin to close andopen said latch;

a trigger including a first arm having a lip thereon adapted forengaging said shoulder to prevent rotation of said cam to close saidlatch unless said sill pin, said hook member and said trigger areproperly positioned with respect to each other, and a second arm adaptedfor engaging said sill pin to remove said lip from engagement with saidcam and permit said rotation when said sill pin, said hook member andsaid trigger are properly positioned with respect to each other; and

an outstanding pin on said hook member adapted for engaging said tab onsaid cover for maintaining said hook in engagement with said sill pinuntil said lip engages said shoulder when said latch is being opened.

1. A latch comprising a sill pin; a rotary eccentric cam having a firstshoulder on the periphery thereof; a hook member mounted on said cam andadapted to move into and out of engagement with said sill pin inresponse to a rotation of said cam to close and open said latch,respectively, a trigger rotatably mounted with respect to said hookmember and having a lip thereon adapted to engage said first shoulder onsaid cam to prevent rotation of said cam to close said latch until saidcam, said hook member and said sill pin are properly positioned withrespect to each other, characterized in that said latch includes: firstmeans for maintaining said hook member in engagement with said sill pinuntil said lip has engaged said first shoulder and until said hookmember has been substantially fully extended when said latch is beingopened; and second means for removing said lip from engagement with saidfirst shoulder after said hook member has moved into engagement withsaid sill pin when said latch is being closed.
 2. Apparatus inaccordance with claim 1 wherein said latch includes: a spring forbiasing said trigger in a direction to cause said lip to engage saidfirst shoulder; a cover having a tab thereon extending outward therefromtoward said hook member; said first means includes a first pin on saidhook extending outward therefrom and adapted to contact said tab toprevent rotation of said hook member with said cam during a substantialportion of said rotation of said cam when said latch is being opened,whereby said cam rotates with respect to said hook member until said lipengages said first shoulder; and said second means includes an arm onsaid trigger adapted to contact said sill pin to pivot said lip awayfrom contact with said first shoulder.
 3. Apparatus in accordance withclaim 2 wherein said hook member includes a second pin extending outwardtherefrom and said cam includes a second shoulder, said first shoulderbeing adapted to contact said second pin to provide a positive rotationforce to said hook member when said hook member encounters resistancebefore said latch is fully open and to prevent further rotation of saidcam in an opening direction when said latch is fully open, and saidsecond pin being adapted to contact said second shoulder to preventfurther rotation of said cam in a closing direction when said latch isfully closed.
 4. Apparatus in accordance with claim 3 wherein said latchis adapted for mounting on doors of a cabinet, said sill pin includes atapered face and said hook member has an end tapered to match said faceof said sill pin and adapted to contact said face to return said hookmember to a position out of engagement with said sill pin when said hookmember is rotated into a position for engaGing said sill pin while saiddoors are open.
 5. A latch comprising, in combination: a latch coverhaving an outstanding tab thereon; a rotary eccentric cam having ashoulder on the periphery thereof; a sill pin; a hook member mounted onsaid cam and responsive to the rotation of said cam to move into and outof engagement with said sill pin to close and open said latch; a triggerincluding a first arm having a lip thereon adapted for engaging saidshoulder to prevent rotation of said cam to close said latch unless saidsill pin, said hook member and said trigger are properly positioned withrespect to each other, and a second arm adapted for engaging said sillpin to remove said lip from engagement with said cam and permit saidrotation when said sill pin, said hook member and said trigger areproperly positioned with respect to each other; and an outstanding pinon said hook member adapted for engaging said tab on said cover formaintaining said hook in engagement with said sill pin until said lipengages said shoulder when said latch is being opened.